High-frequency signaling system



April 12 1927.

Filed Dec. 8. 1921 Patented Apr. 12, 1927.

UNITED STATES 1,624,473 PATENT OFFICE.

LEWIS MASON CLEMENT, OF NEW? YORK, N. Y., ASSIGNOR TG WESTERN ELECTRIC COM- PANY, INCORPORATED, OF NEW YORK, N. Y., A CORTPORATION OF NEW YORK.

HIGH-FREQUENCY SIGNALING SYSTEM.

Application filed December 8, 1921.

This invention relates to duplex transmission systems and more particularly to improved features of such systems whereby the transmitted energy is more perfectly xcluded from the receiver. The invention is more particularly applicable to radio sysif U tems in connection with which it is herein d .-cribed, but the principles of the invention may he applied in other systems than the kind herein described in detail.

in certain types of radio systems for duplex transmission wherein the transmitter and the receiver are connected to an antenna igatcly with respect to each other, it is 1 ble that the energy, which passes into the receiver circuit from the transmitter cuit, be maintained a minimum. The present invention comprises improved meansfor accomplishing this result. In such systems the electromagnetic effect of the transmitter waves on the receiver is balanced as perfectly as possible. Owing to the facility with which high frequency energy is transferred from the transmitting circuit to the receiver circuit by inherent electrostatic coupling, it becomes necessary to reduce the transfer of energy in this manner. F or this purpose an annular or toroidal shield has been provided for the primary of the transformer which transfers energy from the antenna to the receiver circuit. The secondary is mounted in the central portion of the shield, the shield is grounded and a radial slot provided therein to prevent the shield acting as a short circuited secondary for the primary of the transformer. Originally no specific location of this slot was considered essential, it having been placed at any convenient point in the circumference of the shield. In accordance with this invention the radial slot in the shield is placed diametrically opposite to the point on the circumference of the shield which is grounded. It has been found that high frequency current flows from ground into the shield because of the capacity of the shield with respect to other conductive elements in the circuit. The current induced in the shield tends to introduce energy into the coil 10. This causes the transmitter circuit to affect the receiver circuit. By placing the slot opposite to the ground point the capacity currents in the two halves of the shield are equal in amplitude and opposite in phase with respect to the coil 10. For this reason Serial No. 520,846.

their effects in causing unbalance in the primary and secondary circuits or the transfer of energy from the primary to the secondary circuit are neutralized. A further advan tags is secured by placing the axis, upon which the adjustable secondary coil rotates, at right-angles to the plane passing through the slot and the ground connection of the shield.

From a broad viewpoint the invention relates to improved means for shielding a transformer primary from its associated secondary winding.

A further feature consists in the proiion of means whereby variations of impedance of the radiating or aerial part of the antenna will be caused to have a relatively small effect in causing unbalance of the receiver circuit, with respect to the transmitter circuit. The special means employed to accomplish this result consists of a relatively high impedance, for example a small condenser in series with the radiating antenna and a similar impedance in series with the artificial antenna. When a condenser is used in the realantenna circuit and the real artificial antennae are of equal impedance a condenser of similar kind and equal capacity is preferred in the artificial antenna circuit.

The invention will be more particularly described in connection with the accompany ing drawings wherein Fig. l is a view showing in perspective the mechanical arrange- .ment of the shield and the balancing means;

Fig. 2 is a diagram of the primary and secondary windings of the receiving transformer,

Fig. 3 is a simplifiedcircuit diagram and Fig, 4 is a diagram of one convenient form of artificial antenna.

The receiving circuit maybe traced by referring to Figs. 1 and 3: From a'receiving antenna 1 the received high frequency waves are conducted through abinding post 36 into the receiving circuit comprising condenser 12, conductor 3, binding post :26, conductor 4, coil 5, conductor 6, binding post 25, conductor 7, condenserfi, a binding post 36, and the balancing network Alnconstituting an artificial line or artificial antenna, to ground. The received current traversing the coil 5 passes through all the turns in the same direction. That portion ofthe received currentwhich passes through the transmitting circuit 9 will traverse only a portion of the turns of the coil That portion of the received current which p 7, s through all of the coils and that portion of the received current which passes through a portion or the coils acts cumulatively through electromagnetic induction to produce an electromotive force in tne coil it. The tuning condenser 11 shunted around the coil 10 serves to adjust the circuit 10, 11 to resonance at the frequency of the waves being received. The energy in the circuit 10, 11 upon a rcccivin system which may mavenieutly compi :1, a thermionic detector suitable detector device, the output circuit of which connected to any suitable r nslati device such as a telephone recerver. tu ng condenser ll shunted around the con The artificial antenna of vari ble capacity, inductance C, and 7' respectively.

The transmitting circuit comprises a transmitter T which represents any suitable device or system for producing high frequency waves modulated in accordance with signaling waves or impulses. In the present instance it is presumed that the transmitter T constitutes any well-known apparatus for producing speech modulated waves oi radio frequency. High frequency currents produced by the transmitter in the conductor 9, connected to the middle binding post 36 will pass through the turns of the coil 5, part in one direction and part in another. The current through one part of the coil flows through the radiating antenna 1, while the other part will flow through the artificial antenna A in the simplest case if the coil 5 is divided into two similar equal groups of turns and the artificial antenna consists of impedance elements producing an effective r actance and resistance identical with the reactance and resistance of the antenna the effect of the primary current upon the coil 10 will be negligible since the field produced by current in one-halt of the turns oi" coil 5 will be neutralized by that produced by current in the other half of the turns. in this case onehalf of the energy produced by the trans mitter will be consumed in the artificial line. For a short range system utilizing comparatively low power this is not a very serious objection. Less than halt oil: the transmitter energy may be consumed in the artificial an-- tenna by increasing its impedance and resistance relative to that of the antenna and correspondingly adjusting the number of turns in the two parts of the coil 5 so that balance will be secured. ll hen accurate balance is attained the waves generated by the transmitter will produce no diiierence of potential between the plates of the condenser 1%. By varying this condenser it will therefore be possible to tune the antenna for received waves independently of the particular wave length being used for transmis sion. transmission and reception may be c "ried on simultaneously or successively at different wave lengths. Either wave length may be changed within certain limits independently oi the other provided the construction of the artificial antenna is such that reasonably accurate balance is attained for eacl wave length used for transmission.

In order that small changes in impedance of the radiating antenna may not produce correspondingly large increments of unbalance of the receiver circuit with respect to the transmitter circuit a high impedance such a relatively small condenser 2 is provided in series in the antenna circuit. While the artificial antenna Jill might be so designed as to balance the combined reactance of the condenser 2 and the radiating antenna 1 it is preferable to include a condenser 8 in the artificial antenna circuit which is as nearly as possible a duplicate of con denser 2. The ell'ect of the capacity to ground of the elements of the artificial antenna in producing unbalance is thereby largely overcome. The condensers 2 and 8 have equal capacity to ground and have a symmetrical relation with respect to the other elements of the circuit. Every element and lead oi the circuit should be surrounded with a conductive grounded shield in order to secure the best results.

In a radio set adapted for use with antennae such as are used on large vessels the following values of elements have been found practical: Capacity C is variable 'from O to X 10- tarads. Capacities and are 3 X 10 i'arads each with a maxi -um variation of less than 2% from rated value. Coil 5 has 8 double turns of multiple strand insulated wire with the strands separately insulated. Coils am. 10, resistance and condensers 1d and 11 may have any range of values desirable to tune on the diflerent wave lengths to be used. Capacity 1- may be used to change the tuning for reception with a negligible resultant change in the transmitted wave length. The transmitter T will be understood to include suitable capacity and inductive reactances for tuning as well as the elements of a generating and modulating system.

In order to secure balance the conductors 3 and 7 are twisted together and passed through conduit in a shield lead block 19 while the conductors 4: and 6 are twisted together and pass through another conduit in the same block. The conductor 9 is passed through other conduits in the lead block thereby being maintained at the same distances from each member of each of the pairs of twisted conductors. The lead block consists of a body of insulation material comprising any suitablenumber of parts uheld together in anyconvenient manner and .completely surrounded by a shield of con-. Iductive non-magnetic material.

. block is mounted with the'openings of its several conduits adjacent the binding posts.

33, 25, 26 and the condensers 2-and S.

Coil v is wound upon a spool 37 of insulating material, the spool-being provided with flanges 38 to space the coil on all sides away from the surrounding annular shield:

. 39. The shield 39 as illustrated is in the shape of an annulus but may be of any convenient shape totadequately house the coil 5. As used in the specification the term annulus is to be construed as including any shieldhaving substantially the same shape and the function described, such as, for example, atoroidal shield. The shield 390011- ,sists of non-magnetic conductive material,

such aseopper, brass, etc. and is supported to a bracket 40. Brackets 41'0n the shield for the purpose of varying the electromagnetic coupling between the two coils. An arm 42 rigidly attached to the spool upon which the coil is wound moves over a segment 43 to which it may be secured in any desired position of adjustment by a thi'unb screw 44. A radial slot 46 is cut in the shield to break its continuity so that it will not act as a short-circuited secondary for the primary 5. This slot should be comparatively narrow, for example not more than a few millimeters in width, so as 4 to expose as little as possible of the coil 5.

The shield 39 is grounded as illustrated at 45. A convenient ground connection is made by attaching the bracket 40 to a conductive shield 6L7 which constitutes a metal covering for a cabinet in which the receiver is mounted. It has been found that high frequency currents flow into the shield from the ground connection. By placing the radial slot 46 diametrically opposite the grounded bracket 40, these capacity currents will divide equally between the two halves of the shield which are defined by the radial slot and the ground connection. The electrostatic and the electromagnetic effects of these currents on the primary and the secondary are neutralized. A further refinement consists in placing the axis of coil l0 at right-angles to a plane cutting through the annular shield and passing through the slot 46 and the ground connection. A still further refinement consists in winding the coil 5 on the spool 37 in such a manner that all the parts thereof are as nearly as possible spaced equally from the shield. By the aoparatus described the coils 5 and 10 are electrostatically shielded from each other in a very effective manner while at the same time the transfer of energy from The lead the coil 5 to.;the coil. 10. byyelectromagnetic induction is not materially interfered with. Furthermore thecoupling between the two coils can beyadjusted without disturbing the condition of'balance.

This application is a continuation in-part of application Serial No. 430,428'filed December 13, 1920.

The novel features believed to beinherent in the invention are set forth in the appended claims.

-VVhat is claimed is: '1. In a duplex system, a hollow annular shield enclosing a primary winding, means for spacing the'primary from said shield, a slot in the said shield toprevent short circuit currents therein and aground .con-

nection connected to said shield diametrically opposite to said slot.

2. In a signaling system, a substantially annular shaped shield of: conductive material, a spool mounted therein and: an electrical coil wound upon saidspool, said spool being shaped and said coil being wound to space said coil away from the walls of said container, a radial slot insaid container. and a ground connection diametricallyopposite said slot.

3. In a high frequency system, a combination of an annular conductive grounded shield with a coil mounted thereon. and sup ported thereby and a radial slot insaid shieldopposite to the grounded connection.

4:. In a signaling system, a transmitting coil, an annulus like container ofconductive material surrounding and substantially completely enclosing said coil, said container being slotted and a second coil mounted on said container rotatable on an axis at right-angles to said slot.

5. In a signaling system, an electrical coil, an annulus like container of conductive material surrounding and substantially enclosing said coil, a ground connection on said container, said container being slotted diametrically opposite said ground connection.

6. An annulus like conductive shield for an inductance coil having a ground connection and a radial slot directly opposite thereto.

7. A transformer comprising a primary coil, a secondary coil electromagnetically coupled thereto, and means for preventing electrostatic coupling therebetween comprising a conductive shield substantially completely surrounding one winding and excluding the other, said shield having a com- 'plete interruption in its continuity and having a ground at a point diametrically op-. posite said interruption.

8. A transformer comprising electromagnetically coupled primary and secondary windings, a conductive shield substantially enclosing one of said windings and excluding Cil the other, said shield being electrically interrupted in its continuity, and means for mounting the non-enclosed winding for movement about an axis substantially at right-angles to the plane of said interruption.

9. In a high frequency transmission system, a coil of two parts, said parts being mutuaTly inductive, a transmission circuit including one part of said coil, a balancing circuit simulating the impedance of said transmission circuit, and including the second part of said coil, similar high impedances of fixed value located in the transmission circuit and the balancing circuit and a tuning condenser in shunt to said coil whereby the transmission circuit can be timed ithont atl'ecting the reation between said circuit and its balancing network.

10. In a radio circuit for transmitting at a given frequency or frequencies, a coil of two parts, said parts being mutually inductive, an antenna circuit including one part of said coil, a balancing antenna circuit including the other part of said coil, 21 fixed ca iacity of such value as to be out high impedance over the range of frequencies to be transmitted in series with the antenna circuit, a similar high impedance of fixed value in series with the balancing antenna circuit, and tuning means in circuit with said coil whereby the relation between the antenna circuit and the antenna balancing circuit is maintained.

11. In a duplex or two-way radio circuit,

a coil of two parts, said parts being mutually inductive, a radio antenna structure includ ing' one part of said coil, and a balancing antenna structure sin'iuiating the impedance of said radio antenna, including the other part of said coil and capacities of fixed small value in series with said structures and a tuning condenser in circuit with said coil whereby the antenna circuit can be tuned without affecting the relation between said antenna circuit and its balancing network.

12. A radio circuit for simultaneous transmissicn and reception which comprises an aerial circuit, a balancing circuit, identical capacities of fixed small capacity value in each said circuits respectively and means for tuning the aerial ciruit without affecting its relation with said balancing circuit.

18. In a radio system, a rear antenna circuit including a radiating aerial and a condenser,-an artificial antenna circuit for balancing the real antenna circuit comprising inductance, resistance and capacity, the capacity of said artificial circuit being comprised in two condensers, one of which simulates the aerial capacity and is shielded by a grounded shield, the other of which simulates the condenser of the real antenna circnit and is external to said shield.

In witness whereof, I hereunto subscribe my name this (3th day of December, A. D. 1921.

LEWIS MASON CLEMENT. 

